I had an '85 300SD. I got to drive it 8,000 miles before it was Killed in Action at 233,000 miles.
I hadn't had a chance to change the air filter.
The boost was not controlled by computer, it had the usual mechanical injection stuff including spring-valve wastegate and ALDA compensator. No computer chips in the engine bay.
I don't know about differences in transmission pan gaskets, or if there was a California model.
When I bought it I drove it, was impressed by how nice it seemed, and didn't worry too much about much else. I figured I'd deal with problems one at a time.
Having displayed so much ingnorance, I will close by saying that I'd be glad to have to make a choice, and I'd probably just flip a coin. I think either would be great!
Good Luck, Good Hunting and